Field of the Invention
The present invention relates to the technical field of long span structure, particularly, relates to a long span cable-membrane structure, more particularly, relates to a cable-membrane tensegrity structure which is asymmetric and is of an opening type, a method of constructing the same, and a method of designing the same.
Description of the Related Art
Cable-membrane structure, as a novel tension structure, is developed from the late twentieth century. The cable-membrane structure has unique characteristics of structure system, and can make full use of the tensile characteristics of the cable material and the membrane material, increasing the utilization efficiency of materials. The history of the cable-membrane structure may be traced back to ancient tent. However, the ancient tent, as a temporary construction, was not paid much attention to by people before the 80's of last century. After a novel membrane material was developed in the 80's of last century, and the membrane structure is widely applied. According to the construction formation, the membrane structure can be classified as: inflatable membrane structure; cable truss membrane structure; cable dome structure and tension cable-membrane structure.
The tension cable-membrane structure is a structure system depended on tension of membrane and composed of tension cable and the membrane. The tension cable-membrane structure is mainly composed of the tension cable and the membrane material covering on the tension cable. The tension cable can be divided into a valley cable, a ridge cable and a side cable which is at the edge of the membrane. In this kind of structure, the membrane unit is fully tensioned, and can withstand a certain load. This kind structure of membrane unit can serve as a horizontal connection of the structure, has a good bearing capacity, and has a good absorbing effect on the earthquake and the wind load in the horizontal direction.
According to the stress characteristics, the tension cable-membrane structure can be classified as:
(1) A general tension cable-membrane structure, the membrane of which is the main stress part. In this structure, the membrane has certain rigidity by applying a pre-stress to the membrane. Due to limit strength of the membrane itself, a great pre-stress cannot be exerted on the membrane. Thereby, this kind of structure is generally used in small span structure.
(2) A composite tension cable-membrane structure, the cable of which bears the main stress of the structure, and the membrane of which is mainly subjected to local load. Because of the existence of the cable net, this kind of structure has rigidity larger than that of the general tension cable-membrane structure, and it can be used in a large span structure. In addition, in this kind of structure, the pre-stress must be proportionally applied on the cable and the membrane.
The existing cable-membrane tensegrity structure of an opening type is mainly used for the stadium building and mainly comprises two types of (1) The radial cables comprise a lower layer and an upper layer at the outer ring cable and intersect to form one layer at the inner ring cable. The plane is circular or substantially elliptical and has a relatively regular overall configuration. The inner ring cables are in the same plane. (2) The two layers of radial cables intersect to form a circle in the periphery and are divided into two layers at the inner ring cable. The two layers of radial cables are connected by using support bars. As for the above cable-membrane tensegrity structure of an opening type, because of structural constraints, they mostly have a symmetrical shape, and it is difficult to realize an asymmetric shape of the building effect.
Since the tension cable-membrane structure has a beautiful appearance, a lithe and light body, a high material utilization rate, the tension cable-membrane structure is especially suitable for stadium, exhibition venue, airport and other large span structure's roof. With the development of computer technology, the tension cable-membrane structure is developed widely in practical engineering, the cable net in the tension cable-membrane structure functions as the main stress part, and the tension cable-membrane structure is formed by tensioning the membrane as a secondary stress part. Because of the existence of the cable net, this kind of structure has rigidity larger than that of the general cable-membrane structure, and it can be used in the large span structure. In addition, in this kind of structure, the pre-stress must be proportionally applied on the cable and the membrane. The cable-membrane structure of large span is very complex in construction. Thereby, a reasonable construction scheme can not only make the structure formation to meet the design requirements, and can reduce the difficulty of construction process. Different tension construction methods may exert different influences on the stress state of the structure after forming, therefore, the reasonable tension construction scheme relates to the limit stress and the safety performance of the structure.
In the pre-stress cable-membrane tensegrity structure of an opening type, the steel cable is the main force bearing part, and it has a suitable stress characteristics and a high structure efficiency, and can reflect the modern advanced materials, structural system of contemporary architecture design and construction technical level. A whole tension main structure of an opening type consists of two portions (see FIG. 1 and FIG. 4): a continuous tension cable net the dimensional cable-membrane tensegrity structure comprising a central opening and being formed by a suspension cable 1, a ridge cable 2, a valley cable 3 and a ring cable 4; and a surrounding supporting structure 7. Cable membrane secondary structure comprises a membrane side cable 12 and a membrane tensioned on the ridge cable and the valley cable. Pre-stress is applied to the cable net of an opening type so as to convert it from the mechanism to the structure that can withstand the use load. Thereby, the tension cable net is the main stress part of the pre-stress cable-membrane tensegrity structure of an opening type, and it implements the “advanced structural mechanics theory of continuous tension ocean”. This structure system belongs to a nonlinear flexible structure with main characteristics of “small strain-large vertical deformation”.
The pre-stress cable-membrane tensegrity structure of an opening type is very novel, and is restricted by design theory and design means. So far, the design of the pre-stress tensegrity structure is limited to only the elastic stage design, mainly including the member elastic bearing capacity design and the system elastic vertical deformation capacity design. The above design method cannot reflect the whole-process of structural mechanics characteristics from loading to failure, cannot fully reveal security control elements in various stress stages of the structure, and cannot fully meet the pre-stress tensegrity structure safety design requirements. The above design method has been far behind compared with the “elastic-nonlinear” two-stage design method adopted in the conventional construction engineering. Moreover, this kind of structure system belongs to a flexible cable net structure with the main characteristics of the nonlinear large vertical deformation, and the structure response under load is completely different from the mainly rigid structure in conventional construction engineering. Thereby, the current elastic design method cannot reflect the nonlinear large vertical deformation characteristics of pre-stress tensegrity structure of an opening type, cannot achieve the safety control on the bearing capacity and the vertical deformation capacity of the flexible structure, and cannot satisfy the characteristics requirements of the flexible structure system having the characteristics of nonlinear large vertical deformation. Based on the above reasons, the current design method cannot fully meet the safety, the economy and the rationality requirements of pre-stress tensegrity structure of an opening type.